1. Field of the Invention
The present invention relates to an imaging device and imaging method employing a rolling shutter system.
2. Description of the Related Art
In recent years, digital cameras and video cameras using a complementary metal oxide semiconductor (CMOS) imaging device (hereinafter referred to as a CMOS image sensor) have become generally widespread. A CMOS image sensor is structured to output a signal of each pixel by X (vertical) scanning and Y (horizontal) scanning of a group of pixels arranged two-dimensionally, vertically and horizontally.
As a drive method of the CMOS image sensor, a rolling shutter system described in, for example, Jpn Pat. Appln. KOKAI Publication No. 2008-288904 is generally employed. The rolling shutter system is configured to scan a group of pixels arranged two-dimensionally, vertically and horizontally, within one frame period for each line, and sequentially read signals of the pixels.
FIG. 6 is a timing chart showing operation timing of a CMOS image sensor according to the conventional rolling shutter system. In FIG. 6, 1, . . . , n−1, n, n+1, . . . , N are line numbers. Normally, the CMOS image sensor is driven by drive signals consisting of a reset pulse (Vr), redirection pulse (Vrd), and selection pulse (Vsel). That is, in pixels of each line, exposure is started at the input, timing of the reset pulse (Vr), and redirection pulse (Vrd), after that, exposure is terminated at the input timing of the reset pulse (Vr), redirection pulse (Vrd), and selection pulse (Vsel), and then pixel signals of one line are read within a fixed read period 1H set immediately after that.
More specifically, this read period 1H consists of (read period of pixel signals for one line+horizontal blanking period). Further, a period corresponding to (read period×number of lines) is the minimum one frame period of a case of video recording. Accordingly, in video recording, imaging at a higher frame rate is enabled by carrying out thinning-out-reading of thinning out, at regular intervals, lines from which pixel signals are to be read.
However, when video recording is carried out by driving the CMOS image sensor based on the rolling shutter system, the maximum settable exposure time (shutter speed) becomes a time approximately equal to one frame period. Accordingly, the higher the frame rate, the narrower the follow-up range of exposure becomes.